I really found jamuraa’s answer helpful, but going for full xpath gave me a nightmare of a string in my case, so I happily made use of the ability to concatenate find’s in Capybara, allowing me to mix css and xpath selection. Your example would then look like this:
find('#some_button').find(:xpath,".//..").fill_in "Name:", :with => name
Capybara 2.0 update: find(:xpath,".//..") will most likely result in an Ambiguous match error. In that case, use first(:xpath,".//..") instead.